The field of the invention is in the art of temperature control devices.
Thermal switches transferring heat energy from a higher temperature body (a hot body) to a lower temperature body (a cold body, or a heat sink) are well known. U.S. Pat. No. 3,399,717 to patentee R. E. Cline is an example of a state of the art thermal switch.
In many applications equipment, such as electronic devices, must be maintained at or very close to a specified temperature to operator satisfactorily. For example, it is necessary to utilize a close temperature control on oscillator units which generate frequency bands extremely narrow in range. These accurate signals must be maintained over the full operating temperature range of the equipment. Thus, the selected control point is above the maximum anticipated operating temperature. 125.degree.C is a typical value often utilized. For present equipment, however, this upper temperature is very nearly the maximum temperature at which the circuitry is capable of operating reliably. It is desirable to get the electronic equipment up to the designed operating temperature rapidly and quite frequently the heat sink is cold or considerably below this temperature. Under the conditions of a relatively wide temperature difference between the temperature controlled body and the heat sink (or cold body) it is desirable to have minimal thermal coupling so as to reduce the heater load and provide a fast warm-up to temperature. Conventional thermal switches actuated by the temperature of the controlled temperature body cooperating with the conventional proportional heaters within the oscillator can adequately take care of the normal temperature variations and provide satisfactory control. However, under an emergency such as during a dash manuever of an aircraft the cold plate (heat sink) temperatures may momentarily rise quite high so as to approach or even exceed 110.degree.C. Under these conditions the conventional couplings to the heat sink are inadequate and the controlled temperature of the electronics exceed the maximum design temperature of 125.degree.C, the cooling system of the electronic equipment is no longer effective, and the electronic equipment is susceptible to failure at a time it is most urgently needed. When the temperature of the cold plate rises to within approximately 15.degree.C of the controlled temperature point, (typically 125.degree.C), the efficiency of the conventional thermal cooling system is greatly decreased and to provide approximately the same effective cooling requires approximately a thermal impedance reduction by a factory of three between the controlled temperature body and the cold body. Prior to this invention a system having a low thermal impedance at high temperatures of the heat sink and yet provide a large thermal impedance at low and normal temperatures of the heat sink so as to provide rapid warm-up and the minimum of structures and temperatures control equipment has been unknown.